Compounds that inhibit oligosaccharide biosynthesis represent valuable tools for analyzing the role of complex carbohydrates in biological processes. In particular, glycosidase inhibitors such as nojirimycin have been used to dissect specific cellular events and are now being considered as potential therapeutic agents to treat a variety of metabolic and infectious diseases. The goal of the present proposal is to design, synthesize, and evaluate the biochemical and biologic effects of a new class of mechanism-based glycosidase and glycosyltransferase inhibitors. These inhibitor candidates are designed to supply the current need for inhibitors that are both highly potent and selective. The proposed inhibitors are 1-N- iminosugar derivatives, which differ from the currently available inhibitors in possessing a nitrogen atom at the anomeric position of the pyranose ring, which was designed to mimic a model of the beta-glycosidic cleavage reaction intermediate, which has a positive charge on the anomeric position, rather than on the ring oxygen of the sugar. The structure of the proposed inhibitors -- nitrogen in the anomeric position, chair conformation, and appropriate OH substituents to enhance recognition -- is expected to make them highly specific as well as potent against glycosidases. Using this new type of inhibitor with a positive charge on the anomeric position as a probe, the enzyme mechanism will also be better understood. The general synthetic scheme, starting with a readily available carbohydrate derivative, involves i) introduction of an amino functionality, ii) formation of 1-N-iminopyranose ring, and iii) stereoselective introduction of hydroxymethyl group. The 1-N-iminosugar compounds will be further conjugated to a various alkyl groups to be a better inhibitor of glycosidases or an inhibitor of glycolipid synthesis, or to a second sugar moiety to develop sequence-specific endoglycosidase inhibitors. Given the potential specificity and potency of the proposed inhibitors, these reagents are expected to contribute not only to the study of oligosaccharide-mediated cellular events as a new probe but also to the development of inhibitor-based drugs with a wide range of clinical applications.